The interest in obtaining rapid and accurate measurements of photosynthesis in plants and photosynthetic microorganisms has grown considerably with the recent upswing in environmental monitoring and pollution control. In particular, field and agricultural photosynthetic productivity have been examined in terms of how extensively various pollutants, such as acid rain or toxic chemicals, have affected the environment. It is of considerable value to be able to quickly and accurately assess photosynthesis in the field via instruments or methods which are safe and which do not themselves adversely affect the plant life.
The key parameter in any study of environmental effects on photosynthetic activity is the evolved oxygen from the plants. It is well established in this area that the proteins and enzymes associated with light-activated water splitting and oxygen evolution are among the most fragile components of the photosynthetic apparatus. It therefore follows that a careful study of plant oxygen production can serve as an important warning tool in early detection of adverse effects on plants and other organisms caused by environmental pollutants.
One commonly used tool in assessing levels of evolved oxygen is known as a Clark-type oxygen electrode. This electrode, as further described in U.S. Pat. No. 2,913,286 (Clark,Jr.), basically consists of an electrolytic cell having a cathode, an anode, and an electrolytic medium between the two, and is used to polarographically measure the amount of certain substances, such as oxygen, in a solution. The electrolytic medium, however, is separated from the solution to be measured by a selectively permeable membrane barrier, which allows the substance that one desires to measure to enter the electrolyte and thus be measured apart from the compounds in the test solution.
There are many Clark-type oxygen electrodes currently in use, some of which are used to polarographically monitor the evolution of oxygen by plants. One such device is described in Delieu et al., New Phytol, 89:165 (1981), and consists primarily of an electrode chamber employing a Clark-type electrode which is used to assess oxygen production from a circular disc sectioned from a leaf. This device requires the use of a sectioned leaf and thus cannot be used to measure photosynthesis in live leaves. Additionally, this chamber requires an electrolyte solution and an external light source which is projected through the roof of the chamber in order to impinge upon the photosynthetic material.
Other Clark-type oxygen electrodes have been described previously, including U.S. Pat. No. 4,076,596 (Connery et al.), wherein an electrolytic cell for measuring oxygen in a fluid is disclosed having a first and second electrode. Additionally, Phelan et al., Amber. Lab, July 1982, pp. 6514 -72, disclose a Clark-type probe for measuring dissolved oxygen in polluted water samples for use in determining biological oxygen demand, and Friese, J. Electronal. Chem. 106:409 (1980) discloses a Clark electrode which is characterized by a thin layer of ground glass coated with polytetraflourethylene which replaces the membrane barrier. Still other articles are known which disclose use of Clark electrodes in assessing oxygen production, such as Ley et al., Biochimica et Biophysica Acta, 680:95 (1982) and Hale et al., J. Electroanal Chem. 107:281 (1980).
Most of these prior art devices in this area are cumbersome or complex, and are often designated for lab experiments only. None of the presently known Clark-type oxygen electrodes can be used to rapidly and noninvasively take an accurate measure of photosynthetic oxygen production in the field using a live plant source. What is desired, therefore, is to provide a noninvasive, nondestructive device and method to measure in situ photosynthesis rapidly and accurately using live plants.